QUESTION:
Does your program for exposures ever take blury pictures? 

Wayne Baggett writes on May 16:
HST takes excellent images now, since the first servicing mission added the
corrective optics to the various science instruments.  The images we get are
essentially as good as the physics of light will allow in the visible range of
wavelengths, and are only slightly worse in the ultraviolet.  If we ever get
"blurry" images now, it's because the telescope moved during the exposure, and
we can tell this from the information sent down with the image.

Thanks for the questions.  I hope you have enjoyed the Live from HST program,
and have learned some interesting things about how these kinds of projects
really work.  Have a good summer!

Wayne Baggett
Computer Sciences Corporation
Space Telescope Science Institute


ANSWER from Anuradha Koraktar on May 22, 1996:
The blurring phenomenon happens when you take images with the HST of
moving targets and stationary targets. Taking images of a comet for
example is not as easy as taking images of a galaxy because a galaxy
hardly moves during the exposure, but the comet moves and leaves streaks
on the images of the telescope if the telescope is not moved along with
the comet. To eliminate the streaks the telescope works in the gyro mode
and adjusts its pointing according to the speed of the comet's motion.
This exercise is achieved by a process called "guide star hand-over"
Many short exposure images are taken and then added together to
get signal image that can be analysed.